I have the following remarks that are mostly subjective in nature:
1. With the S class, it has a fairly good fit on the mod, and it covers the sharp edges that sometimes we found annoying. However, since it is made essentially for the M class, it is slightly longer than the S class, and this slightly affect the stability of the mod if you put it in an upright position. After a while in that position it will slide up on the mod until it gets to be flush with its bottom. This will cause the buttons (especially the up and down buttons) to be slightly misaligned with the case, but does not impair functionality in any way.
Thought I'd give my opinions, as I have the m series, which differs slightly from the S series. My thoughts are also slightly different then yours... not right or wrong, just I feel differently on some things....
On the M series, the case seems to be a little bit too short. The case would crawl up the bottom of the device, so that the silicon buttons over the bottom button was misaligned. It would still work, but you could see the bottom button peeking out of the cut-out for the usb. Nonetheless, pressing the silicone bottom button would still work. I would tug on the case, and stretch it down, and it would hold for a few hours. This morning, I found it firmly in place and not having moved up the device.
The case has a cutout for the battery insert and the rest of the bottom of the SX. The entire bottom is cut out, with just a narrow outline of silicone outlining the bottom of the device.
2. Naturally the silicone case makes the mod a tad bit larger, and this takes a bit from its ergonomic advantage IMO. It does not feel the same in your grip. One of the things I loved about the SXmini is that it fits just right in my grip (my hands are large).
I don't find the extra size noticeable, but again, everyone is different.
3. The top curve does not have a snug fit with the body of the mod, and accordingly you'll find a soft part above the firing button ..at times some may find this to be rather pleasant.
On the M Series, the top portion fits snuggly.
Finally, while i don't regret getting the silicone case, and i will be on the look out for the black case, it might be better to have a skin wrap of some sort that does not affect the grip and the ergonomics of the mod.
No way do I put a wrap on my SX, especially after seeing the effect it had on the paint of some people's SX after it was removed!
I really wanted a "Shark Skin" type cover, that I could remove when I wanted to see the SX au natural, but that would protect the SX when I was "out and about" and that would give slightly better grip, and this one serves that function! I have to say, it has a GREAT feel in your hand... very soft silicone, very grippy!
I also like having two different looks... grey or black. Having a black silicone case, the device would look nearly the same with or without the case. Perhaps a purple one?
By the way, there is an embossed "SXmini" logo where the logo is on the device, but it's embossed, so it's not very noticeable.